The present invention is directed toward an electric motor of the type that has a primary insulation system to isolate live conductors from portions of the motor that are normally not electrically energized (dead), and a secondary insulation system that isolates those portions of the motor which are susceptable to being contacted by an operator to prevent them from becoming electrically energized should the motor malfunction.
Heretofore, numerous schemes have been used to provide safety protection for motors that operate at sufficiently high power levels to be considered a potential shock hazard to the user should a normally dead conductive material, such as a moor housing, become electrically energized or live. A typical instance of inadvertent energization of a conductive, normally nonenergized material would be having an armature sling a winding to contact the motor housing, which in turn makes the motor housing live. Another instance would be if a brush wears to a point where the brush and/or the brush shunt becomes detached from the brush box and contacts a metal housing or end cap. Another example is to be found in motors wherein brush dust has accumulated in a location that provides an electrically conductive path from a live conductor to a normally nonenergized metal part.
In most motors it is customary practice to first insulate the armature windings from a lamination stack with suitable material, such as fish paper, or a suitable type of epoxy coating. This is considered to be primary insulation. A secondary insulation may then be placed between the lamination stack and the armature shaft so that if the winding should short to the lamination stack, the armature shaft will not become live. Another type of secondary insulation is a metal motor housing covered with an insulating material to prevent inadvertent contact by the user of the motor with a metal housing which may become live.
Other examples of primary insulation of the motor would include the insulation that separates the windings from the armature, the brush rigging from the metal housing or enclosure, such as an end cap, and the insulation that normally separates the various live conductors from the nonenergized metal parts including the power cord to the motor. Secondary insulation is that insulation which prevents physical contact with the normally dead or nonenergized metal part that may become live or energized due to a malfunction of the motor or an additional insulator which would prevent a normally nonenergized metal part from becoming live should the primary insulation fail or an insulator which would prevent operator contact with a normally nonenergized part which has become live.
During assembly of fractional horsepower permanent magnet motors, the positioning of the magnets of the motor relative to the commutated armature is important to obtain peak motor efficiency. One current method of assembling the motor is to adhesively secure ceramic magnets to the interior of the housing, to then heat treat the assembly to cure the adhesive to secure the magnets in position. However, it has been found that this type of assembly process allows possible minor variations to occur and the magnets may not always be secured in the best position to obtain the desired high efficiency of the motor. The herein-described magnet retainer not only provides an insulation layer for providing secondary insulation to the motor, but also provides means for securing a magnet in an identified position and means for orienting the retainer relative to the motor such that the magnets may be assembled to the retainer prior to the retainer being inserted into the housing. The retainer then fixes the magnets in the exact desired position to provide the desired high efficiency operation.